class Solution 
{
    int dx[4] = {0, 0, 1, -1};
    int dy[4] = {1, -1, 0, 0};

public:
    int numEnclaves(vector<vector<int>>& grid) 
    {
        int m = grid.size(), n = grid[0].size();
        vector<vector<bool>> vis(m, vector<bool>(n));
        queue<pair<int, int>> q;

        // 1. 把边上的 1 加入到队列中
        for(int i = 0; i < m; i++)
            for(int j = 0; j < n; j++)
                if(i == 0 || i == m - 1 || j == 0 || j == n - 1)
                {
                    if(1 == grid[i][j])
                    {
                        q.push({i, j});
                        vis[i][j] = true;
                    }
                }

        // 2. 多源 bfs
        while(q.size())
        {
            auto [a, b] = q.front();
            q.pop();
            for(int i = 0; i < 4; i++)
            {
                int x = a + dx[i], y = b + dy[i];
                if(x >= 0 && x < m && y >= 0 && y < n && 1 == grid[x][y] && !vis[x][y])
                {
                    vis[x][y] = true;
                    q.push({x, y});
                }
            }
        }

        // 3. 统计结果
        int ret = 0;
        for(int i = 0; i < m; i++)
            for(int j = 0; j < n; j++)
                if(1 == grid[i][j] && !vis[i][j])
                    ret++;
        
        return ret;
    }
};